Study of needle photo-cathode for bright RF electron gun

In order to develop a stable and high-brightness electron source for the various electron beam applications, improvement of the quantum efficiency and elongation of the lifetime of a photo cathode are important issues. We measured the quantum efficiency of a tungsten needle cathode irradiated by pulse ultraviolet lasers under high electric field. The quantum efficiency steeply when increasing the electric field over 2 GV/m, and exceeded 10% at about 2.6 GV/m. Furthermore, the peak current density emitted from the needle tip of the cathode reached 24 MA/cm2 with the irradiation of 3rd harmonics from a Nd:YLF laser in which the peak intensity was about 800 MW/cm2. (author)